JPH066166A - Piezoelectric vibrator - Google Patents

Abstract

PURPOSE:To select a desired harmonic wave without need for a frequency selection circuit or the like in which no abnormal oscillation takes place by interposing a surface acoustic wave element between a exciting electrode and a lead electrode formed on a piezoelectric substrate so as to form a surface acoustic wave filter. CONSTITUTION:Exciting electrodes 2, 3 are across from each other and form a thickness vibration section D. Either terminal of the electrode 2 has an interdigital transducer 42 and a reflector 43 and connected to a lead electrode via a surface acoustic wave element (SAW) S-4. Furthermore, a lead electrode 6 connecting to the electrode 3 is formed to a back surface of the vibration chip 1. A resonance frequency characteristic for a fundamental wave, a 3rd harmonic wave, a 5th harmonic wave or the like (f1, f3, f5...fn) is provided in the vibrator 1 in each frequency characteristic curve of the vibrator 1 and the SAW 4 in such a piezoelectric vibrator. The resonance frequency fSAW of the SAW element 4 is decided by a line and space of the interdigital electrode. Thus, an optional harmonic fn is selected by constituting the SAW element 4 so that the frequency fSAW is matched with the frequency fn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric vibrator using thickness-shear vibration such as a crystal vibrator, and more particularly, a piezoelectric vibration having a structure capable of selecting a fundamental vibration or an overtone frequency such as third order, fifth order, and seventh order. Regarding the child.

[0002]

2. Description of the Related Art When a vibration condition such as thickness shear vibration of a crystal unit is determined by a thickness t, a vibration frequency f is k.
Is set as a constant and is determined by f = k · 1 / t. As shown in this equation, the vibration frequency is determined by the thickness of the vibrator, and it is necessary to make the vibrator thin in order to increase the vibration frequency.

However, there is a limit to how thin the vibrator can be made, and it is very difficult to mass-produce the vibrator having a fundamental wave of 50 MHz or more.

Therefore, in order to increase the vibration frequency f, it is necessary to use overtone vibration of 3 times, 5 times, etc. of the fundamental wave. When any frequency such as a wave is used, there is a possibility that an erroneous vibration other than the desired frequency may occur.

In order to prevent the above-mentioned malfunction, it is necessary to give the transmitting circuit a severe frequency characteristic, and in some cases to attach an LC circuit in the vicinity of a desired frequency, and it is necessary to add or adjust extra parts. , The configuration becomes large.

For this reason, it is desired to selectively select the vibration mode (fundamental wave, third harmonic wave, fifth harmonic wave, etc.) by the element itself such as the vibrator without depending on the circuit. Research is ongoing.

At present, as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 3-172012 and 3-172013, the positions and shapes of the electrode films provided above and below in the thickness direction,
The method that delicately controls the thickness is the mainstream.

[0008]

As described above, to select a desired mode (fundamental wave, third harmonic wave, fifth harmonic wave, etc.) as the vibration frequency of the piezoelectric vibrator without depending on the circuit, the electrode structure is used. Is used, or the shape of the piezoelectric vibrator is restricted or processed.

However, in these methods, it is difficult to obtain stable quality because a high degree of processing is required, high precision is required, and management is very difficult.

The present invention has been made in view of the above background, and an object of the present invention is to provide a piezoelectric vibrator which has no abnormal oscillation and which can select a desired harmonic without using a frequency selection circuit or the like. And

[0011]

In order to solve the above problems, according to the present invention, an excitation electrode for exciting thickness vibration and an extraction electrode electrically connected to the excitation electrode are formed on a piezoelectric substrate. In the piezoelectric vibrator, a surface acoustic wave filter is formed by interposing a surface acoustic wave element between the excitation electrode and the extraction electrode.

Further, a first excitation electrode and a second excitation electrode, and a first extraction electrode and a second extraction electrode electrically connected to these excitation electrodes are formed on both main surfaces of the piezoelectric substrate, respectively. Also provided is a piezoelectric vibrator, wherein a surface acoustic wave filter is formed by interposing a surface acoustic wave element between the first excitation electrode and the first extraction electrode.

Further, in the above piezoelectric vibrator, the surface acoustic wave filter has a frequency characteristic of selectively outputting a specific frequency from an excitation frequency excited by the excitation electrode. Is also provided.

[0014]

In the present invention, the SAW element having a desired frequency characteristic is formed on the piezoelectric substrate, and abnormal oscillation is suppressed by the frequency selection characteristic of this SAW element, and good frequency characteristic is obtained.

[0015]

1 is a plan view of a frequency selective piezoelectric vibrator according to an embodiment of the present invention. Further, FIG. 2 shows a sectional view of this frequency selective piezoelectric vibrator.

In FIGS. 1 and 2, reference numeral 1 denotes a mirror-finished vibrator piece which is a piezoelectric substrate, 2 is an excitation electrode for thickness-based vibration formed on the upper surface of the vibrator piece 1, and 3 is the vibrator piece 1. Excitation electrodes formed on the back surface of the
3 are formed to face each other, and the thickness vibrating portion D
Are configured.

One end of the excitation electrode 2 has an interdigital transducer 42 and a reflector 43, and has a SAW.
It is connected to the extraction electrode 5 via a surface acoustic wave element (SAW element) 4 that constitutes the vibrating portion S. Further, an extraction electrode 6 connected to the excitation electrode 3 is formed on the back surface of the vibrator piece.

In the piezoelectric vibrator configured as described above, the frequency characteristics of the vibrator 1 are shown in line A of FIG.
The frequency characteristic of the element is shown by the line B. As shown in this figure, the oscillator 1 has resonance frequency characteristics such as a fundamental wave, a third harmonic, a fifth harmonic, etc. (f ₁ , f ₃ , f ₅ , ... F _n ...).

The resonance frequency f _SAW of the SAW element is determined by the line and space of the electrode comb teeth. Therefore, by configuring the SAW element so that this f _SAW matches f _n , it is possible to select an arbitrary harmonic wave f _n .

In this embodiment, the third harmonic f ₃ of the vibrator 1 was selected by constructing a SAW element by matching f _SAW with f ₃ as shown by line A in FIG.

As a result of applying a voltage to the extraction electrodes 5 and 6 from a power source (not shown) to the piezoelectric element according to this example, the frequency characteristic shown in FIG. 4 was obtained.

As shown in this figure, in this piezoelectric element, the fundamental wave f is caused by the frequency selection characteristic of the SAW element 4.
The appearance of harmonics other than ₁ and f ₃ is suppressed, and the third harmonic f
Only ₃ appears, which shows that good frequency characteristics are obtained.

In general, the SAW vibration has a lower Q value than the vibration of the thickness system and the resonance frequency in the vicinity of the admittance peak becomes wider. By adjusting the thickness system resonance frequency f _n in the wide admittance peak, As shown in FIG. 4, both frequency characteristics are combined to obtain a sharp characteristic.

In the present embodiment, the SAW element 4 includes the interdigital transducer 41 and the reflector 42,
The reflectors 42, 43
Can be omitted. In addition, this SAW element 4 is S
The AW element can be formed by a normal manufacturing process, such as a photolithography process.

Further, as the vibrator piece, for example, a crystal vibrator can be used, but other piezoelectric materials can also be used. The holding structure is not particularly limited, and the holding structure can be selected in the same manner as a normal piezoelectric vibrator,
Any holding structure can be used.

[0026]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, by adjusting the frequency selection characteristic f _SAW of the SAW element, it is possible to select an arbitrary higher harmonic wave of the vibrator element and to prevent abnormal oscillation. Can be suppressed.

As a result, when a conventional harmonic wave is used, it is necessary to use a frequency selection circuit or the like as the oscillation circuit, and the number of parts of the circuit is increased and the circuit is enlarged, whereas in the present invention, the oscillation is performed. It is possible to easily realize reduction of the number of components in the circuit, downsizing, high reliability, non-preparation, and the like.

Further, since it is not necessary to delicately adjust the electrode structure, the shape of the piezoelectric vibrator and the like in the processing of the vibrator piece, the design and management can be facilitated and the high reliability can be easily obtained.

[Brief description of drawings]

FIG. 1 is a plan view of a piezoelectric vibrator according to an embodiment of the present invention.

FIG. 2 is a sectional view of a piezoelectric vibrator according to an embodiment of the present invention.

FIG. 3 is a graph showing frequency characteristics of thickness vibration and SAW vibration.

FIG. 4 is a graph showing frequency characteristics of the piezoelectric vibrator according to the embodiment of the invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oscillator piece 2 ... Excitation electrode 3 ... Excitation electrode 4 ... SAW element 5 ... Extraction electrode 6 ... Extraction electrode

Claims (3)

[Claims] 1. A piezoelectric vibrator having an excitation electrode for exciting thickness vibration and an extraction electrode electrically connected to the excitation electrode on a piezoelectric substrate, wherein the excitation electrode and the extraction electrode are provided. A piezoelectric vibrator in which a surface acoustic wave filter is formed by interposing a surface acoustic wave element therebetween. 2. A first excitation electrode and a second excitation electrode, and a first extraction electrode and a second extraction electrode electrically connected to these excitation electrodes are formed on both main surfaces of the piezoelectric substrate, respectively. In the piezoelectric vibrator described above, a surface acoustic wave filter is formed by interposing a surface acoustic wave element between the first excitation electrode and the first extraction electrode. 3. The piezoelectric vibrator according to claim 2, wherein the surface wave filter has a frequency characteristic of selectively outputting a specific frequency from an excitation frequency excited by the excitation electrode. Piezoelectric vibrator.